Fix Python – How to overload __init__ method based on argument type?

Let’s say I have a class that has a member called data which is a list.
I want to be able to initialize the class with, for example, a filename (which contains data to initialize the list) or with an actual list.
What’s your technique for doing this?
Do you just check the type by looking at __class__?
Is there some trick I might be missing?
I’m ….